JPH07277752A - Synthetic quartz glass for ultraviolet light laser and method for producing the same - Google Patents

Abstract

PURPOSE:To provide the synthetic quartz glass capable of being applied to UV light optical parts such as lenses, prisms, beam splitters or spectroscopes, especially optical parts used for the optical systems of UV light laser devices such excimer laser devices, and excellent in optical characteristics, and to pro vide a method for producing the same by a sol-gel method. CONSTITUTION:The synthetic quartz glass for UV light lasers is produced by mixing silica fine particles containing metal elements belonging to the alkali metal elements, the alkaline earth metal elements, and the transition metal elements in concentrations of <=50ppb, respectively, and further Ge, Sn and Pb metal elements in concentrations of <=5ppb, respectively, with a silicone alkoxide containing the metal elements which belong to the alkali metal elements, the alkaline earth metal elements and the transition metal elements in concentrations of <=10ppb, respectively, and further the Ge, Sn and Pb metal elements in concentrations of <=5ppb, respectively, and subsequently subjecting the synthesized gel to a drying, sintering and glassifying treatments under heating.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to optical parts for ultraviolet rays such as lenses, prisms, beam splitters, and spectroscopes, and in particular, optical parts such as lenses and prisms used in the optical system of an ultraviolet laser device such as an excimer laser. The present invention relates to a synthetic quartz glass by a sol-gel method having excellent optical properties applicable to the above and a method for producing the same.

[0002]

2. Description of the Related Art The sol-gel method is known as one of the methods for producing synthetic quartz glass. For example, JP-A-60
In JP-A-215532, a mixed solution of silica sol and silicon alkoxide is gelled under an acidic catalyst to prepare a wet gel, the wet gel is dried to obtain a dry gel, and the dry gel is fired to obtain a transparent quartz glass body. A method of manufacturing is disclosed. As a synthetic quartz glass used as an optical component for ultraviolet rays, for example, quartz glass (Japanese Patent Laid-Open No. 3-5338) in which the concentration of each metal element such as an alkali metal element and a transition metal element is defined is known.

In the quartz glass produced by the conventional sol-gel method, alkali metal elements such as Li, Na and K,
Alkaline earth metal elements such as Mg, Ca, Ti, Fe, N
Since the transition metal elements such as i and Cu are contained, and the absorption of ultraviolet rays by these metal elements and the structural defects in the silica glass induced by these metal elements, the silica glass has 400 n
There is a problem that the ultraviolet transmittance in the wavelength range of m or less is low. Further, when the quartz glass is irradiated with ultraviolet rays having a wavelength of 248 nm, for example, light in the wavelength range of 300 to 450 nm is emitted. It has been known that this light emission phenomenon is caused by a structural defect in the silica glass, which is induced by a metal element contained in the silica glass, but each metal belonging to the alkali metal element, the alkaline earth metal element and the transition metal element is known. It was difficult to suppress the light emission phenomenon only by defining the concentration of the element in the quartz glass. Furthermore, for example, when quartz glass synthesized by the conventional sol-gel method is irradiated with short-wavelength light such as ultraviolet rays, structural defect portions are damaged, and new structural defect species, for example, radical species, are generated, resulting in the optical It may cause deterioration of characteristics.

[0004]

DISCLOSURE OF THE INVENTION The object of the present invention is to transmit ultraviolet rays having a wavelength range of 400 nm or less, not to emit light by ultraviolet ray irradiation, to suppress structural defects in quartz glass, and to use optical glass for ultraviolet lasers, etc. Another object of the present invention is to provide a synthetic quartz glass by the sol-gel method, which is useful for the above, and a method for producing the same.

[0005]

MEANS FOR SOLVING THE PROBLEMS The inventors of the present invention are mainly responsible for the light emission of the respective metal elements Ge, Sn and Pb contained in the quartz glass, and at least Ge, Sn and Pb are used to suppress the light emission. It was determined that the concentration of each metal element of Pb must be 10 weight ppb or less. In addition, even if one of the metal elements belonging to the alkali metal element, the alkaline earth metal element, and the transition metal element has a concentration in the silica glass of more than 100 wt ppb, structural defect species accompanied by induced light emission and metal It was found that the absorption band in the ultraviolet region due to the element causes a decrease in the ultraviolet transmittance of the quartz glass. That is, the concentration of each metal element belonging to the alkali metal element, the alkaline earth metal element, and the transition metal element in the silica glass is 100 weight ppb or less, and each of the Ge, Sn, and Pb metal elements in the silica glass. It is possible to suppress the absorption of light in the ultraviolet region and suppress the emission of light by the ultraviolet light only when the concentration of each is 10 weight ppb or less. Further, it was found that each of these metal elements is mixed in the manufacturing process of quartz glass, and is particularly contained in the silica fine particles and silicon alkoxide which are the raw materials. Furthermore, the present inventors have found that structural defects in the silica glass are generated by the C element present in the silica glass in addition to the above metal elements, and arrived at the present invention.

The present invention is a synthetic quartz prepared by a sol-gel method, which comprises the steps of mixing silica fine particles and silicon alkoxide to synthesize a gel, and drying, sintering and vitrifying the gel while heating the gel. In the method for producing glass, the concentration of each metal element belonging to an alkali metal element, an alkaline earth metal element, and a transition metal element is 50 weight ppb or less, and the concentration of each metal element of Ge, Sn, and Pb is Also, the silica fine particles having a weight of 5 ppb or less. B The concentration of each metal element belonging to an alkali metal element, an alkaline earth metal element, and a transition metal element is 10 weight ppb or less, and each of the metal elements Ge, Sn, and Pb is A method for producing a synthetic quartz glass using as a raw material a silicon alkoxide having a concentration of 5 ppb or less,
Further, the present invention uses silicon alkoxide as a main raw material,
In the synthetic quartz glass obtained by the sol-gel method,
An alkali metal element contained in the synthetic quartz glass,
The concentration of each metal element belonging to the alkaline earth metal element and the transition metal element is 100 weight ppb or less, and G
The synthetic quartz glass for ultraviolet laser has a concentration of each metal element of e, Sn and Pb of 10 weight ppb or less and a C element concentration of 30 weight ppm or less.

In the present invention, examples of the silicon alkoxide used as a raw material include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane and the like, with tetramethoxysilane and tetraethoxysilane being preferred.
An alkali metal element contained in silicon alkoxide,
The concentration of each metal element belonging to the alkaline earth metal element and the transition metal element is 10 weight ppb or less, preferably 1 weight p.
It is necessary that the concentration of each of the metal elements Ge, Sn, and Pb be 5 wt ppb or less, preferably 1 wt ppb or less. The transition metal elements referred to in the present invention are elements having atomic numbers 21 to 30, 39 to 48, 57 to 80 and 89 or more. To reduce the metal concentration in the silicon alkoxide, for example, a method of distilling with a distillation apparatus made of high-purity quartz glass can be mentioned.

The concentration of each metal element belonging to the alkali metal element, the alkaline earth metal element and the transition metal element contained in the silica fine particles used in the present invention is 50 weight pp.
b or less, preferably 20 weight ppb or less, and Ge,
The concentration of each metal element of Sn and Pb is 5 weight ppb or less,
It is preferably required to be 1 ppb or less by weight. Further, the shape of the silica fine particles is spherical, and the particle diameter is 0.1 to 10.
It is preferably 1 μm. In such silica fine particles, the concentration of each metal element belonging to the alkali metal element, the alkaline earth metal element, and the transition metal element is 10 weight ppb or less, and the concentration of each metal element of Ge, Sn, and Pb is Can be synthesized by hydrolysis and dehydration polycondensation reaction of a silicon alkoxide having a weight of 5 ppb or less. That is, spherical silica fine particles having a particle diameter of 0.1 μm to 1 μm can be synthesized by a method of dropping the silicon alkoxide under a stirring condition in a mixed solution of water, alcohol and an aqueous ammonia solution. The concentration of each metal element belonging to the alkali metal element, the alkaline earth metal element and the transition metal element contained in the water, alcohol and aqueous ammonia solution used at this time is 10 wt ppb or less, preferably 1 wt ppb or less, and Ge The concentration of each metal element of Sn, Pb and Sn is 5 weight ppb or less, preferably 1 weight ppb or less.

As a method for producing synthetic quartz glass by the sol-gel method using the silica fine particles and silicon alkoxide as raw materials, known methods can be adopted. For example, the following method can be adopted. desirable.
Disperse silica fine particles in water or a liquid containing water,
A so-called silica sol solution is prepared. The concentration of each metal element in water or a liquid containing water used at this time is preferably 1 weight ppb or less, for example, ultrapure water having an electric resistance value of 17.5 MΩ or more.

The pH of the prepared silica sol solution is adjusted to about 2 with an acidic aqueous solution under stirring conditions. Subsequently, 0.1 to 1.0 mol of silicon alkoxide is added to 1 mol of silica fine particles in the silica sol solution to hydrolyze the added silicon alkoxide. After that, the pH is adjusted to 4 to 5 with a basic aqueous solution under stirring conditions to carry out the dehydration polycondensation reaction. When the mixed solution after adjusting the pH is poured into an appropriate container and kept at room temperature, it gels in several hours to obtain a gel (wet gel). The acidic aqueous solution and the basic aqueous solution to be used are preferably hydrochloric acid aqueous solution and ammonia aqueous solution, respectively, and the concentration of each metal element belonging to the alkali metal element, the alkaline earth metal element and the transition metal element is 10 weight ppb or less. , Preferably 1 weight p
The concentration of each metal element of Ge, Sn, and Pb is 5 wtppb or less, preferably 1 wtpp or less.
b or less. When such hydrochloric acid aqueous solution and ammonia aqueous solution are commercially available, they can be used as they are.

In the steps from preparation of the silica sol solution to obtaining the gel, alkali metal elements such as Na, alkaline earth metal elements such as Ca and transition metal elements such as Fe are contained in the silica fine particles and silicon alkoxide as the raw materials. Except for those described above, it is easy to mix in particles floating in the air, the container used, and the like, and Sn and the like are easily mixed in from a plated device and the like. Therefore, in order to strictly exclude the mixing of each metal element, the steps from the preparation of the silica sol solution to the preparation of the gel are referred to as class 10000 (class according to US Federal Standard 209D, and the number of the class is 0.5
The concentration of airborne particles of μm or more (representing the number of particles / ft ³ ) is performed in a clean room that is dust-free, and as a container used for gel synthesis, the amount of metal elements eluted by acids and bases is as small as possible. For example, containers made of high-purity quartz glass, Teflon, polyethylene, etc. are used, and the solution stirring device is a device that does not scatter metal abrasion powder from the sliding part of the motor part, such as a Teflon rotor. And using a magnetic stirrer. By doing this, the maximum amount of each metal element mixed from the environment and the container is 3
It can be suppressed to 0 weight ppb or less, and particularly for each metal element such as Ge, Sn, and Pb to a maximum of 3 weight ppb or less.

This wet gel is dried for a suitable time to give a dry gel, which is then heated to about 1800 ° C. for sintering and vitrification to obtain transparent synthetic quartz glass. The carbon concentration in this synthetic quartz glass is 3
In order to make it 0 ppm by weight or less, at least 200-
Within the temperature range of 500 ° C. in an oxygen-containing gas atmosphere,
The treatment is performed for 0 hours or longer, preferably 300 hours or longer. The step of drying the gel is performed in a clean room that is dust-free compared to class 10000, and the inner wall is covered with resin or quartz glass in order to suppress the mixing of metallic elements such as Fe from the inner wall of the dryer used. By doing so, the mixing of metal elements is eliminated as much as possible. In addition, dry gel 18
The heat treatment to 00 ° C. is preferably performed in a high-purity gas such as oxygen, nitrogen, argon, or helium, while circulating these gases, or under reduced pressure. The gel to be heat-treated is placed on a jig made of quartz glass, a jig made of high-purity carbon, or the like so as not to come into direct contact with the furnace material or the like.

The synthetic quartz glass produced in this manner has a concentration of each metal element belonging to the alkali metal element, the alkaline earth metal element and the transition metal element contained in the quartz glass of 100 weight ppb or less. , And Ge,
The concentration of each metal element of Sn and Pb is 10 weight p
Quartz glass having pb or less, C concentration of 30 ppm by weight or less, transmitting ultraviolet rays having a wavelength range of 400 nm or less, and not emitting light by ultraviolet ray irradiation.

[0014]

[Function] An alkali metal element contained in quartz glass,
By setting the concentration of each metal element belonging to the alkaline earth metal element and the transition metal element to 100 weight ppb or less and the concentration of C element to 30 weight ppm or less, absorption of ultraviolet rays by these metal elements and these Generation of structural defects in silica glass induced by a metal element or C element can be suppressed, and by setting the concentration of each metal element of Ge, Sn, and Pb to 10 weight ppb or less, emission can be suppressed, and 400 nm The synthetic quartz glass which has good transmittance in the following ultraviolet region and which does not emit light by irradiation with ultraviolet rays can be obtained.

[0015]

EXAMPLES The present invention will be specifically described below based on Examples and Comparative Examples. Examples 1 to 3 and Comparative Examples 1 to 9 A methanol solution having a composition of 8 mol / liter of water and 1.5 mol / liter of ammonia was prepared in a polyethylene reaction vessel, and tetramethoxysilane was added under stirring conditions with a magnetic stirrer. 1 mol of 1 liter of a methanol solution was dropped to synthesize a silica sol solution containing silica fine particles. Next, the solution content in the silica sol solution was evaporated to adjust the silica fine particle content in the silica sol solution to 30% by weight. An aqueous hydrochloric acid solution was added to the silica sol solution in the polyethylene reaction vessel under stirring conditions with a magnetic stirrer to adjust the pH to 2.0, and then tetramethoxysilane was added to cause hydrolysis. Further, an aqueous ammonia solution was added to adjust the pH to 5.0. After adjusting the pH, the silica sol solution was transferred to a predetermined Teflon container. The silica sol solution gradually increased in viscosity, and gelled in about 2 hours after pH adjustment to obtain a wet gel. Work from silica sol synthesis to gelation is class 1000
I went in a clean room.

The wet gel obtained was classified into Class 1000.
In a dryer placed in a clean room of 0, the gel was dried stepwise by heating to 200 ° C. to obtain a dry gel.
This was placed in a quartz glass container installed in an electric furnace. Approximately 38 up to 900 ° C while circulating oxygen after filtering with a 0.2 μm filter in a quartz glass container.
The remaining solution components were removed by heating stepwise over 0 hours. Then, the gel, which has been heated up to 900 ° C., is transferred into a high purity carbon container installed in a vacuum electric furnace, and the gel is heated from 900 ° C. to 1300 ° C. at 1 × 10 ⁻² Torr.
The transparent synthetic quartz glass is heated stepwise in the following reduced pressure atmosphere for about 150 hours, and further gradually heated from 1300 ° C to 1800 ° C in the high purity argon gas atmosphere for about 10 hours. Created.

The concentrations of the tetramethoxysilane used, methanol, an aqueous ammonia solution, an aqueous hydrochloric acid solution, the silica fine particles in the synthesized silica sol, and the respective metal elements in the synthesized quartz glass were determined by inductively coupled plasma-mass spectrometry (ICP-).
MS) method was used for analysis. The lower limit of analysis of ICP-MS is 1 weight ppb or less for all elements to be analyzed. The Sn concentrations in the methanol, ammonia aqueous solution, and hydrochloric acid aqueous solution used in all Examples and Comparative Examples were 2 wtppb, 2 wtppb, 1 wtppb, and Pb concentrations were 1 wtppb, 1 wtppb, and 2 wtppb, respectively. , G
The e concentration was 1 weight ppb in all, and the concentration of each of the other metal elements was 5 weight ppb or less.

The concentration of each metal element belonging to the alkali metal element, the alkaline earth metal element and the transition metal element is 10 weight ppb or less, and the concentration of each metal element of Ge, Sn and Pb is 5 weight ppb or less. When a silica sol is synthesized using tetramethoxysilane which is, the concentration of each metal element belonging to the alkali metal element, the alkaline earth metal element and the transition metal element in the silica fine particles is 50 weight ppb or less, and Ge , Sn and Pb each had a concentration of 5 weight ppb or less.
Table 1 shows each metal concentration in the silica glass synthesized by using tetramethoxysilane having various concentrations of each metal element as a raw material and silica fine particles synthesized by using them.
The concentration of each metal element belonging to alkali metal elements, alkaline earth metal elements, and transition metal elements is 10 weight pp
b or less and the concentration of each metal element of Ge, Sn, and Pb is 5 weight ppb or less, and the concentration of each metal element belonging to an alkali metal element, an alkaline earth metal element, and a transition metal element In the examples, silica fine particles having a metal content of 50 ppb or less and a metal element concentration of Ge, Sn and Pb of 5 ppb or less are used as raw materials. The other cases are shown as comparative examples.

The carbon concentration in the synthesized quartz glass was adjusted to about 2000 by high-frequency induction heating of the quartz glass in an oxygen stream.
The measurement was performed by heating to 0 ° C. and quantifying the desorbed carbon dioxide. The carbon concentration in the silica glass synthesized by heating the gel to 900 ° C. over 380 hours was 30
It was less than ppm by weight. The carbon concentration in the silica glass synthesized by heating the gel to 900 ° C. for 50 hours and 10 hours was 50 ppm by weight and 100 ppm by weight, respectively.
It was m.

In order to evaluate the optical characteristics of the obtained quartz glass, the quartz glass was optically polished into a 12 mm × 12 mm × 20 mm prism. The ultraviolet transmittance of 200 to 400 nm and the emission spectrum by ultraviolet excitation of 248 nm were measured. In order to evaluate laser resistance, quartz glass is irradiated with KrF excimer laser light under conditions of irradiation energy density of 50 to 400 mJ / cm ² and total irradiation pulse number of 1 × 10 ⁵ , and electron spin resonance (ESR). Using the above method, the radical species produced in the quartz glass by laser irradiation were observed as an ESR signal. Table 2 shows the evaluation results of ultraviolet transmittance, luminescence intensity and ESR of the quartz glass.
It was shown to. Quartz glass, in which the concentration of at least one of the metal elements belonging to the alkali metal elements, alkaline earth metal elements, and transition metal elements in the quartz glass exceeds 100 weight ppb, is absorbed in the ultraviolet wavelength range of 200 to 400 nm. It was not possible to obtain quartz glass having a band and good ultraviolet transmittance. In addition, Ge, Sn and Pb in quartz glass
Among the respective metallic elements, the quartz glass in which the concentration of at least one element exceeds 10 weight ppb is
It had an emission band in the wavelength range of 00 to 500 nm.

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

Industrial Applicability According to the present invention, there is provided a synthetic quartz glass excellent in laser resistance, which transmits ultraviolet rays having a wavelength range of 400 nm or less and does not emit light upon irradiation with ultraviolet rays and which suppresses the amount of structural defects in the quartz glass. It has become possible to manufacture. The synthetic quartz glass according to the present invention is used as an optical component for ultraviolet rays such as a lens, a prism, a beam splitter, and a spectroscope, particularly as an optical component such as a lens and a prism used in an optical system of an ultraviolet laser device such as an excimer laser. It is applicable.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Naoya Hoe, 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Inside Advanced Technology Research Laboratories, Nippon Steel Corporation (72) Hatsushi Inoue 2-18 Shimogusa, Suginami-ku, Tokyo -17 (72) Inventor Tetsuhiko Takeuchi 3-3-5 Yamato, Suwa, Nagano Seiko Epson Corporation

Claims (3)

[Claims] 1. A synthetic quartz glass produced by a sol-gel method, which comprises steps of mixing silica fine particles and silicon alkoxide to synthesize a gel, and drying, sintering, and vitrifying the gel while heating the gel. A method for producing a synthetic quartz glass for an ultraviolet laser, which comprises using the following fine silica particles and a silicon alkoxide in the production method. a The concentration of each metal element belonging to the alkali metal element, the alkaline earth metal element and the transition metal element is 50 weight ppb or less, and the concentration of each metal element of Ge, Sn and Pb is 5 weight ppb or less. Some silica fine particles. b The concentration of each metal element belonging to the alkali metal element, the alkaline earth metal element, and the transition metal element is 10 weight ppb or less, and the concentration of each metal element of Ge, Sn, and Pb is 5 weight ppb or less. A silicon alkoxide. 2. The method for producing synthetic quartz glass according to claim 1, wherein the silica fine particles are synthesized by hydrolysis of silicon alkoxide and dehydration polycondensation reaction. 3. A synthetic quartz glass obtained by a sol-gel method using silicon alkoxide as a main raw material, and each metal belonging to the alkali metal element, alkaline earth metal element and transition metal element contained in the synthetic quartz glass. The concentration of each element is 100 weight ppb or less, and G
A synthetic quartz glass for an ultraviolet laser, characterized in that the concentration of each metal element of e, Sn and Pb is 10 weight ppb or less and the concentration of C element is 30 weight ppm or less.